List Rates

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is fully covered. The description adds useful domain context — these are retail pay-as-you-go prices resolved per destination country — but says nothing about whether historical rates are retrievable, currency/units of the returned prices, or result size. Modest value on top of annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single tight sentence with the key qualifier ('pay-as-you-go retail') front-loaded and no filler. It is efficient, though the terseness edges toward under-specification for a five-parameter tool.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description should convey what a 'rate' record looks like (price, currency, unit, destination) and how asOfDate/direction shape the result; it conveys none of that. Annotations cover safety, but an agent still cannot predict the response shape or the meaning of three of five parameters from this definition.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is only 40%, so the description has to compensate, and it partly does: it expands the `type` enum into words and reinforces `market` as the home market. However, `asOfDate`, `direction`, and `servingCountry` are never explained in the description, and 'per destination country' is ambiguous since no destination parameter exists — the closest is servingCountry, which the schema labels as the roaming location.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific resource (pay-as-you-go retail rates), its scope (home market), and the variants covered (international voice/SMS/MMS, roaming data, per destination country). It is a noun phrase with no explicit verb, but combined with the 'List Rates' title an agent can tell this is a rate-lookup tool rather than a usage or line tool. No sibling is directly overlapping, so no differentiation is needed.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no statement of when to use this tool versus the many other listing tools (list_usage, list_user_plans, search_capabilities), nor any prerequisite or exclusion. Usage is only inferable from the resource name. An agent must guess whether this is for pricing lookups before ordering plans or for explaining charges.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.